This is the kind of sparsely plotted comedy that depends on compelling characters, but it stars two young actors defined by ironic detachment.

People with high blood pressure need romantic comedies, too, and their cardiologists will be very grateful for “Nick & Norah’s Infinite Playlist,” a scrubbed-up, nearly somnambulistic night tour of teen-hipster Manhattan. This is the kind of sparsely plotted comedy that depends on compelling characters, but it stars two young actors defined by ironic detachment. Michael Cera and Kat Dennings may bring some young behinds to theater seats, but the number will be finite, as the pic’s energy level is too low for breakout B.O.

That said, it’s refreshing to see a youth-oriented comedy that doesn’t presume its audience has attention deficit disorder, and that believes editing should be determined by a sense of logic, or even by music. “Nick & Norah’s Infinite Playlist” (no connection, or reference, to Dashiell Hammett’s Nick and Nora Charles) strives to give its characters emotional breathing room. Cera, doing what he’s done in “Juno” and “Superbad,” plays Nick, alt-rock bassist, high school student and ex of the evil Tris (Alexis Dziena), for whom he spends his days making moony mix CDs. Norah (Dennings), who despises Tris and adores this unknown boyfriend who makes the mix CDs, has no luck at love. But she’s recognized on sight by every nightclub doorman in the East Village and Brooklyn (her pedigree is kept secret until later), and her ability to cut lines is equaled only by Nick’s ability to find a parking space for his taxi-yellow Yugo, directly in front of any place he and his posse happen to be going. (This is a fantasy, of course, so one shouldn’t be persnickety about motor-vehicle sci-fi.)

In the hands of director Peter Sollett (whose acclaimed 2002 indie, “Raising Victor Vargas,” took a less glamorous view of Gotham) and scribe Lorene Scafaria (adapting a novel by Rachel Cohn and David Levithan), the romantic direction in which the film is headed is never a mystery.

Nor is it a mystery that a movie like this is inevitably going to be dependent on its peripheral characters: The standout is Ari Graynor as Caroline, Norah’s cocktail-guzzling pal, who spends most of the film in a drunken tizzy, trying to navigate dance floors and, ultimately, the Port Authority Bus Terminal. There,pic reaches its aesthetic low point when Caroline fishes her cell phone and chewing gum out of a toilet that might have been borrowed from “Trainspotting.”

The characters spend much of the movie hunting down a band called Where’s Fluffy, whose whereabouts are teased on the radio (in what seems to be a reference to “American Graffiti”), sending Nick, Norah and their pals on an inter-borough hunt. Along the way, Nick and Norah are both tempted by ex loves — Nick by Tris, and Norah by the opportunistic Tal (Judd Apatow regular Jay Baruchel).

This is a formula film, inasmuch as Nick and Norah initially have all the chemistry of Clorox and ammonia but gradually warm to each other, realizing the depths of their simpatico worldviews and musical tastes.

It’s also a film for tourists — there are so many glistening skylines, beautiful people and landmark commercial institutions , all shown in glossy advert style, that, in terms of promoting New York tourism, “Nick & Norah’s Infinite Playlist” makes “Sex and the City” seem like “Fort Apache: The Bronx.” It’s sweet, no doubt, but a bit too slick for its own good.